What the OASIS trial semaglutide data tells you — and what it doesn't

What the trial actually measured, and why the two weight-loss figures are both true

A number that comes up regularly in coverage of oral semaglutide is 17% weight loss. It is not wrong, but it needs context. The OASIS 4 trial reported two figures: an average reduction of about 13.6% across all participants regardless of how consistently they took the medicine, and a figure of around 16.6% (often rounded to 17%) among those who stayed fully adherent throughout the 64 weeks. Both are from the same study; neither is inflated. The distinction matters because real-world adherence is rarely perfect.

The trial enrolled 307 adults who had a BMI of 30 or above, or 27–29.9 alongside at least one weight-related condition such as high blood pressure or raised cholesterol, and who did not have type 2 diabetes. Participants followed a reduced-calorie diet and increased their activity levels alongside the medicine, conditions the MHRA licence reflects. A common misconception worth setting aside gently: the trial was not testing the tablet against the weekly injection. OASIS 4 was placebo-controlled, so the headline figures describe what the tablet does against no active medicine, not how it ranks against Wegovy's injection or tirzepatide. For a head-to-head comparison of semaglutide versus other treatments, the evidence from the Wegovy clinical programme is a better starting point.

The gastrointestinal side-effect pattern in OASIS 4 was consistent with other GLP-1 trials: nausea, vomiting, diarrhoea and constipation were the most frequently reported, occurring in 74% of the treatment group versus 42% on placebo. Most were mild to moderate in intensity and tended to ease as participants adjusted to the medicine. The NHS patient information for semaglutide sets out the full side-effect profile in plain language.

How the trial evidence shaped the MHRA licence, and what that means for eligibility

Regulatory agencies do not approve medicines based on one study. The OASIS 4 data sat alongside earlier phase 2 OASIS findings and the broader semaglutide development programme before the MHRA granted approval on 11 June 2026. The resulting UK licence for Wegovy tablets covers adults with a BMI of 30 or above, or 27–29.9 alongside at least one weight-related condition, used alongside a reduced-calorie diet and increased physical activity. Lower BMI thresholds can apply for some ethnic backgrounds under UK guidance, your prescriber will confirm what applies to you.

It is worth being clear about what the licence does not cover. Wegovy tablets are not licensed for type 2 diabetes; that is the territory of Rybelsus, a different oral semaglutide product with different doses. The Wegovy tablet schedule runs 1.5mg to 4mg to 9mg to 25mg, the dose strengths associated with Rybelsus (3mg, 7mg, 14mg) are not part of the weight-loss tablet programme. For anyone already established on the 2.4mg weekly injection, moving to the tablet is a clinical conversation, not a straightforward swap, and requires prescriber review. If you want to explore what Wegovy as a treatment involves more broadly, that page covers both forms.

One practical advantage the OASIS trial population experienced: the tablet requires no refrigeration. Room-temperature storage makes it easier to keep the routine consistent, which matters given that adherence is one of the variables that separates the 13.6% average from the 17% fully-adherent figure. If you want to understand more about how the semaglutide trial programme was designed and what it means for people starting treatment, that page sets out the key details. Whether that trade-off suits your life is part of what a consultation explores.

Turning the evidence into a personal decision

Trial data gives you population averages. A prescriber gives you an individual assessment. The OASIS figures are robust (a randomised, placebo-controlled phase 3 study is the standard clinicians and regulators rely on) but they cannot tell you whether oral semaglutide is appropriate given your medical history, current medicines, or specific circumstances. A prescriber at a GPhC-registered service reviews those details before any prescription is issued. That review is not a formality; it is where the population data gets translated into your situation.

People sometimes ask whether the trial results mean oral semaglutide is better or worse than the weekly injection. The short answer is that OASIS 4 was not designed to answer that. For those weighing the two routes, the detailed OASIS 4 page and the STEP 1 trial findings for the injection sit alongside each other and give you the most useful comparison. Cost context is another factor for many people; a straightforward breakdown of weight-loss treatment options and how private pricing works is worth reading before you make a decision.

The MHRA's approval of Wegovy tablets as part of its expanding semaglutide authorisations reflects a body of evidence that now includes multiple trial phases, injection and tablet forms, and new indications. That context does not change the fundamental step: a GPhC-registered prescriber needs to assess whether this treatment is right for you before any prescription is written. If you want to find out whether you meet the criteria, you can check your eligibility with our clinical team through a free consultation.